Nope. BMW has stated very clearly that engine/component sharing is the key way to drive costs down and increase per vehicle profitability and meet fuel efficiency goals, including the M cars. So the customer is in fact getting lower cost components relative to what they're paying. With BMW's current regime, there will be no bespoke M engines going forward (which is completely different philosophy from the 'guy who got fired'). Mind you this isn't from BMW marketing folks, blogs, automotive magazines or anything, this is right from their publicly available investment presentations/transcripts and what they're telling shareholders. The "left over" from engine budget is going right to shareholder equity. M vehicles will be more profitable going forward, but at whose expense?

Do you realise what kind of budget is needed to develop a from scratch engine?

If you did, you would know that using an existing engine would leave plenty in reserve to give shareholders a better margin and spend serious cash on 'engineering'.